Electromagnetic tracking systems are useful in medical device applications where the position and orientation of a medical device can often provide useful information in a minimally invasive or surgical medical procedure. Such systems often include a set of electromagnetic field generators (e.g., field transmitters) and one or more field sensors associated with a medical device that can measure signals from the set of transmitters. The measured signals are used with a computational algorithm to estimate the position and/or orientation of the medical device or a portion thereof (for example, the distal tip of a medical device).
Conductors (e.g., metals) in the environment of an electromagnetic tracking system can cause tracking errors, given that the transmitted field may be distorted in the presence of conductors. The transmitted fields can drive eddy currents in metals or other conductors in the environment around the transmitters, and these eddy currents in turn result in distortions of the transmitted fields. In procedures requiring a high degree of accuracy in position and/or orientation tracking, such field distortions can result in errors in position or orientation that negatively impact the medical procedure. It is therefore desirable to seek methods to suppress or mitigate such errors due to conductors in the environment of an electromagnetic tracking system.
While there have been previous attempts to address this problem, there is a need for a direct and simple-to-implement solution that does not place significant constraints on the hardware of a tracking system and does not result in significant additional computational demands. For example, conventional systems typically attempt to mitigate these types of errors by calibrating the system based on mathematical models of the distortion that are dependent upon properties of the particular conductors present in the environment. This approach is inflexible, as a change in the presence, position, orientation, etc., of conductors in the environment requires an evaluation of those conductors and an adjustment of the transmission parameters based on that evaluation, which also increases computational costs.